The major aim of the proposed population-based case-control study is to compare levels of vitamin A, vitamin E, and selenium in stored sera collected in 1974 in individuals who subsequently developed colon cancer with serum levels in controls from the same population who did not develop cancer. A secondary aim is to examine the relationship of dietary intake of vitamin A and vitamin E to serum levels in both cases and controls. Study subjects will be selected from among participants of the serum collection campaign (Operation CLUE) done in Washington County, Maryland in 1974. Colon cancer cases who were first diagnosed from January 1, 1975 to the present will be ascertained from the Washington County Cancer Register. It is estimated that there will be approximately 70 cases. Two controls will be matched to each case on the basis of age, sex, and month of Operation CLUE participation. A food frequency questionnaire will be administered in-person to study subjects to determine past frequency of eating foods containing high amounts of vitamin A, B-carotene, other carotenoids, vitamin E, fiber, and fat. The questionnaire will be pilot tested among participants of a 1971 study which included a food frequency questionnaire. Mean serum levels of vitamin A, vitamin E, and selenium will be compared in cases and controls. The correlation of dietary intake of vitamin A and vitamin E with serum levels will be determined; it is likely that the sample size will not be sufficiently large for observed differences in dietary intake of nutrients between cases and controls to attain usual levels of statistical significance. Demographic and socio-economic characteristics will be studied and their effects as well as effects of dietary intake of fat and fiber, if any, will be controlled in the comparison of serum levels of nutrients.